The present invention relates generally to annular parts of the type commonly referred to as diaphragms, used mainly in clutches and particularly in diaphragm clutches for motor vehicles.
As is known, an annular diaphragm of this kind generally comprises a peripheral portion which is circularly continuous, and which forms a resilient washer of the Belleville washer type adapted to act on a pressure plate in order to clamp a friction disc between the latter and a reaction plate, and a central portion which is circularly fragmented to form radial segments by means of slots extending radially from a respective blind end near the said peripheral portion to an open end and leading in each case into a central aperture common to all the said slots. The central portion is adapted to control a deformation of the resilient washer formed by the said peripheral portion so as to effect the release of the pressure plate by the washer under the action of an axially movable clutch release bearing, which for that purpose acts on the free ends of the radial segments constituting the diaphragm.
At the present time the slots dividing the central portion of a diaphragm of this type are usually made by a cutting-out operation in a press, this cutting being effected with the aid of punches, each of which simultaneously forms the two edges of a slot.
The inevitable result is that circumferentially a slot formed in this manner has a width corresponding very accurately to the width of the punch producing it.
Having regard to the inherent characteristics of the blank undergoing punching, and particularly the high elastic limit of this blank, which is for example of the order of 80 kg/mm.sup.2, its great hardness which is of the order of e.g. 200 to 250 HB, and its not negligible thickness of the order of e.g. 2 to 3 mm, the punches used for cutting a blank of this kind must necessarily be extremely robust to have an acceptable life, and must therefore necessarily have circumferentially a width greater than a critical threshold value, which is usually fixed at about 1.5 mm, unless they are made of expensive special steels and/or are used at reduced working speeds.
In practice this has the consequence that the slots dividing the central portion of a diaphragm into radial segments usually have at the present time a circumferential width at least equal to 1.5 mm.
However, these slots reduce the total supporting surface offered to the clutch release bearing by the central portion of the diaphragm on which the said release bearing has to act, this supporting surface being reduced to that presented to the said clutch release bearing by the radial segments separated by each pair of slots.
This inevitably results in correspondingly greater wear on the surfaces actually in contact between the clutch release bearing and the ends of the radial segments on which the release bearing acts.
In order to overcome this shortcoming it has already been proposed, particularly in French Pat. No. 1,398,920, to give a reduced width to the slots in question over at least part of their radial length including their open end, in order thereby to increase at this location -- which corresponds to the support presented to the associated clutch release bearing -- the supporting surface provided for the release bearing.
Nevertheless, for the reasons explained above this arrangement has hitherto encountered practical difficulties in its application, so that it has in fact never been possible to utilise it industrially.
The general object of the present invention is the provision of a process and an apparatus suitable for producing such slots of reduced width; it has as a further object the provision of the annular part -- in practice a clutch diaphragm -- obtained by the application of a process of this kind.